Heinrich and his team discovered a circular feature while studying a topographic map of the area off of Hwy. 37, a geologic formation that would not likely have occurred naturally in an area like that of St. Helena Parish, with no volcanoes or salt domes.
Heinrich says the meteor is estimated to have measured about 100 feet in diameter. The crater is about one mile across. While no fragments of the meteor have been discovered—with as much as 90% likely to have vaporized upon impact and the remaining pieces destroyed by weathering--the iron-rich sediments comprising the rim of the crater appear to have been fractured and bleached along these fractures by super-heated water. Microscopic analyses of quartz sand from the rim of the crater found “shock marks” typical of hypervelocity impacts in the form of shocked quartz, which is created only by meteor strikes and nuclear tests, and intensely fractured quartz.
The St. Helena crater is the only known meteor crater in Louisiana and one of only 176 on earth. This type of meteor impact occurs once every 2000-6000 years.
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Coarse grain of shocked quartz from the site of the Brushy Creek meteor crater in St. Helena Parish.
Exposure showing fractures that occur within sediments comprising rim of the Brushy Creek Crater near Greensburg, Louisiana. Whitish to greyish colors along fractures are possibly the result of bleaching of iron-stained sediments by superheated water along fractures. Sand from the sediments at this location consists of intensely fractured sand and innumerable grains of shocked quartz.
Excerpt from the Greensburg 7.5-minute USGS topographic map illustrating the circular rim of the Brushy Creek Crater in St. Helena Parish.